Retinoic acid (vitamin A acid), an active metabolite of vitamin A, has extremely important physiological functions, e.g., differentiation of immature cells under development processes toward mature cells having specific functions, enhancement of cell proliferation, and life support action. It has been revealed that various vitamin A derivatives synthesized so far also have similar physiological functions, for example, the benzoic acid derivatives disclosed in Japanese Patent Unexamined Publication (KOKAI) Nos. (Sho)61-22047/1986 and (Sho)61-76440/1986 and the compounds described in Journal of Medicinal Chemistry, 1988, Vol. 31, No. 11, p.2182. "Retinoids" is a general term for retinoic acid and the aforementioned compounds having retinoic acid-like biological activities.
For example, it was proved that all-trans retinoic acid binds as a ligand to the retinoic acid receptor (RAR) present in cell nuclei, which belongs to the intranuclear receptor super family (Evans, R. M., Science, 240, p.889, 1988), and regulates proliferation and differentiation of animal cells or cellular mortalities (Petkovich, M., et al., Nature, 330, pp.444-450, 1987). It has also been suggested that the aforementioned compounds having the retinoic acid-like biological activities, e.g., 4-[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)carbamoyl]benzoi c acid: Am80, also bind to RAR in similar manners to retinoic acid to exhibit their physiological actions (see, Hashimoto, Y., Cell Struct. Funct., 16, pp.113-123, 1991; Hashimoto, Y., et al., Biochem. Biophys. Res. Commun., 166, pp.1300-1307, 1990). Clinically, these compounds were found as useful for the therapeutic and preventive treatment of vitamin A deficiency disease, hyperkeratosis of epithelial tissue, rheumatism, delayed allergy, bone disease, leukemia and certain types of cancer.
Compounds are known which antagonize against these retinoids and reduce the primary actions of the retinoid (Eyrolles, L., et al., Journal of Medicinal Chemistry, 37(10), pp.1508-1517, 1994). However, a compound has not been known, other than those disclosed in EP 694,301 A1, which enhances the actions of the retinoids such as retinoic acid, while the compound, per se, has no retinoid action or its retinoid actions are negligible. In this publication, it is suggested that a ligand compound specific to RXR receptor has an enhancing activity on Am80, i.e., a ligand specific to RAR-.alpha.-receptor.